1. Field of the Invention
The present invention relates to a system for treating polychlorobiphenyls to render them harmless by decomposing them.
2. Background of the Invention
Heretofore, polychlorobiphenyls (hereinafter abbreviated to "PCBs") have been widely used in the field of chemical industry. Since PCBs are characterized by having low heat capacity and good insulation properties, they have been used as insulating oils for condensers, transformers, etc., and for heat transfer media and the like. In recent years, however, it was found that PCBs are not only injurious to the human body but also bioconcentrated when absorbed in the human body. For this reason, the production and use of PCBs were prohibited by law in 1972 in Japan, and incineration at high temperatures was established as only one safety method for the disposal of PCBs. However, when PCBs are disposed under inadequate conditions, there is such a possibility that virulently poisonous dioxin is generated. It is therefore difficult to find good locations for incinerators for disposing PCBs. In Japan, it has been reported that about 5,500 tons of PCBs were incinerated in 1988-1989 by Kaneka Corp., and this is only one report on the disposal of PCBs. It is the present situation in Japan that there is little prospect of the disposal of PCBs. Since 1993, the possessors of PCBs, which cannot be subjected to disposal, are obliged to take custody of PCBs by notification from the Ministry of International Trade and Industry.
Under the aforementioned circumstances, studies are now being made on a method for rendering PCBs harmless by using a technique other than the above-described one. Hitherto, there have been proposed a method in which PCBs are changed into biphenyl, for instance, by causing dechlorination reaction by the use of photochemical means, a method in which PCBs are decomposed by microorganisms such as Pseudomonas, and a method in which PCBs are chemically decomposed by utilizing supercritical water. When PCBs are treated by one of these methods, there is no fear that dioxin is generated.
For example, in a method in which PCBs are decomposed by utilizing dechlorination reaction induced by ultraviolet-light irradiation, the progress of the dechlorination reaction has been generally confirmed by taking a reaction solution irradiated with ultraviolet light out of a reactor for carrying out dechlorination reaction, subjecting the reaction solution to such pretreatments as concentration and the removal of substances which will hinder the quantification of the PCBs, and quantifying the PCBs existing in the reaction solution by means of gas chromatography or the like.
However, in the above-described method for quantifying PCBs, it is necessary to take a reaction solution out of the reaction system, and also the pretreatments are complicated and require time, so that it has been difficult to continuously determine the progress of the decomposition reaction at real time.
To solve the aforementioned problems, there has been proposed, as described in Japanese Patent Laid-Open Publication No. 262171/1994, a unit which is provided to a device designed for decomposing halogenated organic compounds by using ultraviolet light, and which is used to measure the quantity of the decomposed residue of the organic compounds by obtaining the absorption spectrum of the reaction solution at real time. However, many of halogenated organic compounds have absorption bands in the ultraviolet region. It is therefore difficult to independently quantify, by using the absorption spectrum, the reaction products or intermediate products produced by complicated reactions, and the desired compound. Thus, there is yet room for improvement in this method.
Further, a video fluorescent monitor for determining the contour of spilt PCBs or PCB mineral oil is described in the specification of WO 93/13404. In this specification, it is described that a split of an insulating oil containing PCBs used for a transformer or condenser is observed by the fluorescent monitor. However, this fluorescent monitor is designed for observing the fluorescence of the mineral oil as a whole, and not for quantifying a specific compound, that is, PCBs contained in the mineral oil.
Japanese Patent Laid-Open Publication No. 304407/1994 describes a device for rendering injurious chlorine compounds harmless. In this publication, it is described that the undecomposed residue of PCBs is detected by an apparatus for monitoring the decomposition of PCBs. However, any specific method for measuring the quantity of the PCBs is not found in this publication.